There should be a fair number of impressions of those kinds of things that survive that long. Paleontologists find fossilized footprints from early man, dinosaurs, and other animals from time to time. However, impressions of other objects may not be recognizable to future paleontologists.
In a low oxygen environment, which mud often is, such things as keys or bottle caps will survive millions of years. They have found a few bits of soft tissue from dinosaurs, for example. However, the envronment has to stay low oxygen for that survival so anything disturbing it will result in those things rusting/rotting away.
At high pressure deep in the Earth, diamond is the stablest form of carbon. So as long as it’s down there, it’s not going to degrade. But at or near the surface, diamonds are only metastable and the stablest form of carbon is graphite. Heat up a diamond enough (but short of the point of combustion) and diamond will spontaneously convert to graphite. At temperatures we’re comfortable with, diamonds will eventually convert as well, but it’ll take a long time. Basically, it has to tunnel through a kinetic energy barrier to convert. I don’t think anyone knows the halflife for this, so it may be longer than a few million years.
The Leo 1 dwarf galaxy will have been watching “Star Trek” and “Lost in Space” episodes for almost 180,000 years by then. Plenty of time to prepare for our invasion. They are not going to fall for that “We come in peace” BS when they see us killing aliens in every episode.
Thanks for the replies, very interesting. Here is what I think:
Cut diamonds: as most diamonds are cut into brilliants, with identical number of faces, I wonder if the intelligent beings in 5 My. will identify them as artificial. They might think: diamonds usually cristallize octahedrally, but sometimes they form many facets with a symmetrical circular arrangement. Plus diamonds tend to be minuscule, are very rare even today and they burn easily. Perhaps, if diamonds are mostly found together with gold it will be more obvious that they are artificial.
Glass items. Looks promising. Perhaps if Marmite and Bovril glasses are kept together they may believe they are male and female shells and not artificial? Telefone displays etc. look good to me.
Stone tools are a very good idea. Mortars and pestles in all sizes could become coveted collectors items Tombstones would be something too: they tend to come in rows togehter, that hint strongly at artificial.
Impressions are very helpful, thanks a lot, Quercus!
I have my doubts about the 1990 Hondas, I mean, not even the Volkswagen Beetle rolls forever… But the sediment layer with AOL CDs is promising.
Teeth with goldfilling! Excellent, thanks a lot, Hari_Seldon! I guess titanium replacement hips and knees would last quite long too, they usually get carefully buried (together with the tombstones).
Does anybody have any idea how long rubber can last under anaerobic conditions and sheltered from the light? I am thinking about rubber tires.
Tombstones would be something too: they tend to come in rows togehter, that hint strongly at artificial.